Updated side panel UI (improved)

Updated side panel for Data, Actions, and Events to include add/edit/delete buttons and select lists. Obviously non-functional.
https://www.cs.drexel.edu/~sb679/Waved/ to view.

There are some differences between what I did and what the prototype has:
1. For actions and events I included the word "Actions" and "Events" for consistency with the Data section. We can remove these later if we don't like them.
2. I added edit buttons that were missing from the prototype.
3. I use icons instead of +/- because there is no simple character for edit.

Covers https://github.com/KSHSK/WAVED/issues/26 and https://github.com/KSHSK/WAVED/issues/27 plus the data section which didn't have an issue.